Electrically-controllable reflecting devices are known, for example from Japanese patent publication no. 52-40215, wherein the reflecting device comprises a mirror mounted on two or more arms of piezoelectric material, possibly flexible piezoelectric material, which upon application of an electrical voltage between the upper side and the lower side of the crystal material causes the arms to bend slightly. If the crystal materials are connected in pairs to the applied voltage in counter-phase, the mirror will tilt, and thus it is possible to electrically control the tilting of the mirror both with regard to the extent of the tilt and its direction. If four crystals in cruciform configuration are used, the mirror can be controlled so that an incident beam of light can be reflected as desired. The deflection of the mirror is, however, quite small, in that the maximum deflection of the crystal is in the order of 0.05 mm to each side, and the practical use of such devices is therefore strongly limited. In order to increase the deflection of the mirror, and to make it possible to use a thicker and herewith a more solid but also heavier mirror, a number of crystal elements can be mechanically coupled in series, which is known for example from U.S. Pat. No. 4,660,941. However, this results in a mechanically complicated construction, and while the possibility is no doubt provided of greater mirror deflection, the deflection on the other hand is considerably slower, which for some applications is totally unacceptable.
From U.S. Pat. No. 3,981,566, a deflection device is known which has a flexible and bendable coupling part disposed between the crystal and the mirror, so that the stiff deflection of the crystal elements can be transferred to the mirror by a kind of hinge effect. This results, however, in a certain attenuation, so that for many applications the speed of the deflections is inadequate. Similarly, the amplitude of the deflection is limited to the amplitude of the crystal.
The whole of the known technique in this field has limitations with regard to the magnitude of the tilting of the mirror, even though attempts are made, as disclosed in U.S. Pat. No. 3,981,566, to allow the deflections of the crystal elements to be transferred to the mirror as closely as at all possible to its center.
The object of the invention is therefore to increase the deflection of the mirror as much as possible, and hereby extend the possibilities of application for such devices.
This is achieved by configuring the instrument according to the invention in that sufficient energy is constantly applied to the mechanical oscillation system for the resonant oscillations to be maintained at one or more of the system's resonant frequencies. This results in the deflection of the mirror or the mirrors being multiplied many times, depending on the efficiency of the oscillation system. By constructing the mechanical oscillation system in different ways and with the use of different materials, it can be configured so that it assumes one or more resonance frequencies of the desired extent and amplitude, depending on the application for which the instrument is to be used.
By configuring the deflection instrument according to the invention as disclosed and characterized in that the movable elements are not all supplied with electrical signals or voltages of the same frequency, the possibility is provided of generating almost any oscillation pattern for the mirror or the mirrors, and one can hereby make a beam of light which is directed onto the mirror or the mirrors, after reflection from said mirror or mirrors, describe almost any desired path.
The deflection instrument according to the invention can be configured as disclosed and characterized in that the movable elements are piezoelectric crystal elements, so-called bimorph actuators, in that this hereby enables the construction of a very compact instrument which is easy to "pump" with oscillation energy, while at the same time control the direction of the mirror's mechanical oscillations.
The deflection instrument according to the invention can also be configured as disclosed and characterized in that the movable elements are electromagnetic elements, or elements coupled to electromagnetic elements. This manner of applying energy to the oscillating system is particularly suitable if several mirrors are to oscillate in step with one another, but moreover has the advantage that it does not demand operational voltages as great as those necessary for the crystal elements.
By configuring the deflection instrument as disclosed and characterized in that in the light path in front of the instrument there is disposed at least one rotating mirror and possibly one or a number of stationary mirrors, the reflected light can be made to spread itself over a very much greater area, which is particularly advantageous if the instrument is used for the generation of laser-sweep patterns, e.g. for the reading of line codes for example on goods at a cash terminal, in that with this configuration a high sweep-rate as well as a large deflection can be achieved, and at the same time herewith control over the shape of the pattern.
The invention also relates to a controllable reflecting device which can be used in deflection instruments as described above. By configuring the reflecting device as disclosed and characterized above, the possibility is provided of maximizing the deflection and of a relatively simple assembly process for the mirror, which is normally glued directly to a rubber or plastic mounting. The possibility is also provided of achieving more uniform products, and by the selection of the type of plastic or rubber one can change the characteristics of the mirror system with regard to resonant frequencies and quality. By configuring or disposing the plastic or rubber cylinder asymmetrically or as a rectangular cylinder instead of a circular cylinder, one can generate various resonant frequencies in different directions.
The invention also relates to a controllable reflecting device which can be used in deflection instruments as described above. By configuring the controllable reflecting device as characterized above, the possibility is provided of achieving a very precise tilting or deflection of the mirror without any significant harmonics. Moreover, the characteristics of the mechanical oscillation system can be varied by the use of balls of different sizes, by the use of different binding materials etc.
By configuring the controllable reflecting device according to the invention as disclosed and characterized in that the movable elements are elongated, substantially rectangular piezoelectric crystal elements with a short side facing towards the mirror and offset for substantially half of their breadth in relation to the central area of the mirror, the possibility is provided of achieving a very large deflection, in that it becomes possible to dispose the balls closely to each other and close to the center of the mirror, so that a maximum mirror deflection is achieved for a given deflection of the crystal elements.
By configuring the controllable reflecting device according to the invention as disclosed and characterized in that four elongated, substantially rectangular piezoelectric crystal elements are used, these being arranged in pairs in parallel and with coincident longitudinal axes, the possibility is provided of producing it as a very small and slim construction, for example so that the whole of the reflecting device can be disposed in a tube with an opening for the light.
By configuring the controllable reflecting device according to the invention as disclosed and characterized in that the piezoelectric crystal elements are not all of the same length, different resonance frequencies can be generated in different directions in a simple manner, so that the reflected light can be made to describe a path with a desired form or direction.